I hardly ever play games, but I found this and now regularly play it between tasks. It doesn't have the amazing graphics of modern games, but it's gameplay is so simple that it's highly addictive.
You start as a small cell and by grazing some small dots you can become bigger. By hitting space you can divide which will make the other half spurt in the direction of your mouse cursor. This allows you to eat smaller cells. The goal is to become bigger and bigger.
Do mind, there are many users with offensive names, that can be really terrible (think about world leaders that are known to have killed many, illnesses and swear words) I hope the developer will blacklist those, but as the game is only a couple of days old, this seems not to have been a priority (yet).
(Oh and try to find me, I play as Myce.com )